Digitonin, a saponin having well-recognized pharmacological properties, is commonly obtained by extraction from plants of the genus Digitalis, particularly from seeds of Digitalis purpurea. The primary extract is typically purified by precipitation with cholesterol to yield a mixture of digitonin and digitonin-related saponins. Owing to the difficulty of separating digitonin from this mixture, the purified extract is generally employed in pharmaceutical applications, rather than purified digitonin.
While effective, these purified saponin extracts have several disadvantages as a pharmaceutical. The low solubility of the saponins in aqueous solution makes them difficult to administer. The compounds are fairly toxic, typically producing acute inflammation in parenteral administration and exhibiting strong hemolytic effects. The reported LD.sub.50 of digitonin in rats by i.v. administration is 4 mg/kg. The digitonin property of forming insoluble complexes with cholesterol has been employed pharmaceutically to regulate cholesterol adsorption in humans, as exemplified by U.S. Pat. No. 4,242,502 to Malinow, et al. However, this same property has been implicated in the toxic side effects experienced in parenteral administration of digitonin and digitonin-related saponins.